One requirement for a display device such as a liquid crystal display device is many-gray-level display, whereas a display device (e.g., liquid crystal display panel) itself may not be adapted to the required many-gray-level display. For example, there is a case in which 8 bits are allocated to each of red (R), green (G), and blue (B) in original image data, whereas the display device may be adapted to image data in which 6 bits are allocated to each of red (R), green (G), and blue (B).
One approach for addressing such mismatching is to perform a color reduction process. The problem of the mismatching of the number of the gray-levels between the image data and the display device can be solved by performing the color reduction process on multi-gradation image data (in which 8 bits are allocated to each of red (R), green (G), and blue (B), for example) to generate image data adapted to the number of gray-levels of the display device (in which 6 bits are allocated to each of red (R), green (G), and blue (B)), and driving the display device in response to the color-reduced image data. Especially, when an FRC (frame rate control) is adopted in the color reduction process, this effectively increases the number of gray-levels in a pseudo manner, enabling displaying an image with an improved image quality.
Such a technique is disclosed in, for example, Japanese Patent Application Publication No. P2002-287709A. In a liquid crystal display device disclosed in this publication, the color reduction process is performed in an MPU, and the color-reduced image data are transferred to a liquid crystal drive circuit. The liquid crystal drive circuit drives a liquid crystal display panel in response to the image data having been subjected to the color reduction process. In addition, Japanese Patent Gazette No. 3735529 discloses a liquid crystal display device in which image data obtained by an error diffusion process including an FRC process in an error diffusion processing circuit are transferred to a signal electrode drive circuit.
The color reduction process effectively reduces the data size of the image data to some extent, which is preferable in data transfer. The reduction in the data size of image data effectively reduces electric power necessary for the data transfer. The color reduction process, however, only achieves a limited effect of reducing the data size, and therefore the effect of reducing power necessary for data transfer is also limited.
In order to further reduce the data size of image data to be transferred, it is effective to perform a compression process on the image data, and transfer the compressed data obtained by the compression process. Such a technique is disclosed in, for example, Japanese Patent Application Publication No. P2006-303690 A. This publication discloses a technique in which compressed data obtained by compressing image data are stored in an image memory, and compressed data read from the image data are decompressed and then transmitted to a display device.
According to investigation by the inventors, however, there is room for improvement in the above-mentioned techniques, in terms of simultaneously achieving reduction in power necessary for transfer image data and improvement in the image quality of an image displayed on a display device.